Low dose whole brain RT has demonstrated safety in many studies, and the investigators will be using even lower doses. These lower radiation therapy doses have a history of excellent success for patients with non-cerebral amyloidosis, and have had durable response combined with the necropsy / neurocognitive testing in genetically altered Alzheimer's disease mouse model, the investigators decided to proceed with a human trial, using fractionated whole brain radiation doses of 2.0 Gy x 5, then 2.0 Gy x 10. Subjects will be followed with neurocognitive testing at 6 weeks, 3, 9 and 12 months post RT. Additionally, given that the development of supranuclear cataract has been reported in a high percent of AD patients, the investigators will recommend ocular testing at baseline and at 1 year to assess a potential abscopal effect, collateral benefit to the non-targeted lenses from treatment of the primary disease in the brain.